97 research outputs found
Poole-Frenkel Effect and Phonon-Assisted Tunneling in GaAs Nanowires
We present electronic transport measurements of GaAs nanowires grown by
catalyst-free metal-organic chemical vapor deposition. Despite the nanowires
being doped with a relatively high concentration of substitutional impurities,
we find them inordinately resistive. By measuring sufficiently high
aspect-ratio nanowires individually in situ, we decouple the role of the
contacts and show that this semi-insulating electrical behavior is the result
of trap-mediated carrier transport. We observe Poole-Frenkel transport that
crosses over to phonon-assisted tunneling at higher fields, with a tunneling
time found to depend predominantly on fundamental physical constants as
predicted by theory. By using in situ electron beam irradiation of individual
nanowires we probe the nanowire electronic transport when free carriers are
made available, thus revealing the nature of the contacts
3D Simple Monte Carlo statistical model for GaAs nanowire single photon avalanche diode
GaAs based nanowire single photon avalanche diode (SPAD) has been demonstrated with extremely small afterpulsing probability and low dark count rate, and hence it has attracted wide attention for the near infrared applications. However, there is a lack of model to accurately evaluate the avalanche breakdown performance in nanowire SPAD with a spatially non-uniform electric field. In this work, we have developed a three-dimensional (3D) Simple Monte Carlo statistical model for GaAs nanowire SPADs. Model validation includes ionisation coefficients of GaAs and avalanche gain in GaAs nanowire avalanche photodiode. We also apply our model to predict the device performances of breakdown probability, mean time to breakdown and timing jitter, which are essential parameters for SPAD design. Simulating a PN junction GaAs nanowire SPAD design using our model, we found that device performances have little dependence on the primary carrier injection type, but the nanowire doping concentration requires optimization for high performance SPAD design and operation
Ultracompact bottom-up photonic crystal lasers on silicon-on-insulator
Abstract Compact on-chip light sources lie at the heart of practical nanophotonic devices since chip-scale photonic circuits have been regarded as the next generation computing tools. In this work, we demonstrate room-temperature lasing in 7 × 7 InGaAs/InGaP core-shell nanopillar array photonic crystals with an ultracompact footprint of 2300 × 2300 nm2, which are monolithically grown on silicon-on-insulator substrates. A strong lateral confinement is achieved by a photonic band-edge mode, which is leading to a strong light-matter interaction in the 7 × 7 nanopillar array, and by choosing an appropriate thickness of a silicon-on-insulator layer the band-edge mode can be trapped vertically in the nanopillars. The nanopillar array band-edge lasers exhibit single-mode operation, where the mode frequency is sensitive to the diameter of the nanopillars. Our demonstration represents an important first step towards developing practical and monolithic III-V photonic components on a silicon platform
Bottom-up Photonic Crystal Lasers
The directed growth of III–V nanopillars is used to demonstrate bottom-up photonic crystal lasers. Simultaneous formation of both the photonic band gap and active gain region is achieved via catalyst-free selective-area metal–organic chemical vapor deposition on masked GaAs substrates. The nanopillars implement a GaAs/InGaAs/GaAs axial double heterostructure for accurate, arbitrary placement of gain within the cavity and lateral InGaP shells to reduce surface recombination. The lasers operate single-mode at room temperature with low threshold peak power density of ~625 W/cm^2. Cavity resonance and lasing wavelength is lithographically defined by controlling pillar pitch and diameter to vary from 960 to 989 nm. We envision this bottom-up approach to pillar-based devices as a new platform for photonic systems integration
Electro-optical and lasing properties of hybrid quantum dot/quantum well material system for reconfigurable photonic devices
We characterize the electro-optical and lasing properties of a hybrid material consisting of multiple InAs quantum dot (QD) layers together with an InGaAs quantum well (QW) grown on a GaAs substrate. Over 40 nm Stark shift of the InGaAs QW leading to 9 dB extinction ratio was demonstrated. Lasing operation at the QD first excited state transition of 1070 nm was achieved and together with < 10 ps absorption recovery the system shows promise for high-speed mode-locked lasers and electro-modulated lasers. (C) 2013 American Institute of Physics. (http://dx.doi.org/10.1063/1.4791565
Carrier localization and in-situ annealing effect on quaternary Ga1-xInxAsySb1-y/GaAs quantum wells grown by Sb pre-deposition
Using temperature-dependent photoluminescence spectroscopy, we have investigated and compared intrinsic InGaAs, intrinsic GaInAsSb, and p-i-n junction GaInAsSb quantum wells (QWs) embedded in GaAs barriers. Strong carrier localization inside the intrinsic GaInAsSb/GaAs QW has been observed together with its decrease inside the p-i-n sample. This is attributed to the effect of an in-situ annealing during the top p-doped AlGaAs layer growth at an elevated temperature of 580 degrees C, leading to Sb-atom diffusion and even atomic redistribution. High-resolution X-ray diffraction measurements and the decrease of both maximum localization energy and full delocalization temperature in the p-i-n QW sample further corroborated this conclusion. (C) 2013 American Institute of Physics. (http://dx.doi.org/10.1063/1.4795866
Review Article: Molecular Beam Epitaxy of Lattice-Matched InAlAs and InGaAs Layers on InP (111)A, (111)B, and (110)
For more than 50 years, research into III–V compound semiconductors has focused almost exclusively on materials grown on (001)-oriented substrates. In part, this is due to the relative ease with which III–Vs can be grown on (001) surfaces. However, in recent years, a number of key technologies have emerged that could be realized, or vastly improved, by the ability to also grow high-quality III–Vs on (111)- or (110)-oriented substrates These applications include: next-generation field-effect transistors, novel quantum dots, entangled photon emitters, spintronics, topological insulators, and transition metal dichalcogenides. The first purpose of this paper is to present a comprehensive review of the literature concerning growth by molecular beam epitaxy (MBE) of III–Vs on (111) and (110) substrates. The second is to describe our recent experimental findings on the growth, morphology, electrical, and optical properties of layers grown on non-(001) InP wafers. Taking InP(111)A, InP(111)B, and InP(110) substrates in turn, the authors systematically discuss growth of both In0.52Al0.48As and In0.53Ga0.47As on these surfaces. For each material system, the authors identify the main challenges for growth, and the key growth parameter–property relationships, trends, and interdependencies. The authors conclude with a section summarizing the MBE conditions needed to optimize the structural, optical and electrical properties of GaAs, InAlAs and InGaAs grown with (111) and (110) orientations. In most cases, the MBE growth parameters the authors recommend will enable the reader to grow high-quality material on these increasingly important non-(001) surfaces, paving the way for exciting technological advances
Strongly coupled slow-light polaritons in one-dimensional disordered localized states
Cavity quantum electrodynamics advances the coherent control of a single
quantum emitter with a quantized radiation field mode, typically piecewise
engineered for the highest finesse and confinement in the cavity field. This
enables the possibility of strong coupling for chip-scale quantum processing,
but till now is limited to few research groups that can achieve the precision
and deterministic requirements for these polariton states. Here we observe for
the first time coherent polariton states of strong coupled single quantum dot
excitons in inherently disordered one-dimensional localized modes in slow-light
photonic crystals. Large vacuum Rabi splittings up to 311 {\mu}eV are observed,
one of the largest avoided crossings in the solid-state. Our tight-binding
models with quantum impurities detail these strong localized polaritons,
spanning different disorder strengths, complementary to model-extracted pure
dephasing and incoherent pumping rates. Such disorder-induced slow-light
polaritons provide a platform towards coherent control, collective
interactions, and quantum information processing.Comment: 17 pages, 5 figures and supplementary informatio
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